Silliness is playful, lighthearted behavior that doesn't take itself seriously. When your little brother makes funny faces at the dinner table, that's silliness. When friends start giggling uncontrollably over a joke that wasn't even that funny, they've descended into silliness.

Silliness means doing things just for fun, without worrying about looking foolish or being perfectly sensible. A silly person might wear mismatched socks on purpose, invent ridiculous rhymes, or pretend to be a penguin while walking across the playground. There's an innocent, carefree quality to silliness: it's not mean-spirited or harmful, just goofy and fun.

The word can describe both behavior and content. A silly movie has absurd jokes and impossible situations. A silly question might be “Do fish get thirsty?” It's not a stupid question, exactly, just one that shows playful thinking rather than serious inquiry.

Sometimes adults tell kids to “stop being silly” when it's time to focus on serious work, but silliness itself isn't bad. Everyone needs moments of silliness to release tension and enjoy life. The key is knowing when playfulness fits the situation and when it's time to be serious.